X-Axis pose flip does not work properly in part of armature
Ok, it seem a problem with roll of your UpperArm_L bone, it isn't mirror of its counterpart. 


Go to edit mode of your armature.
Select the UpperArm_L Bone.
Click the Bone tab.
set the Roll from -162.7d to 39.86d.
This would offset all child bones, do the above changes to roll for Forearm_L(35.73d), then WristIK_L(49.01d), then Wrist_L(50.17d) copy the negative of Right side roll. (Do it in said order)
All set to go.